/**
 * Extends layout with map $extension.
 * @param  {Map}    $extension              Map with additional layout settings.
 * @param  {String} $layout-key: 'default'  Key of layout to be retrieved and returned after extension.
 * @return {Map}                            Returns extended layout map for $layout-key.
 */
@function layout-extend($extension, $layout-key: default) {
  @if (type-of($extension) != map) {
    @return false;
  }
  $LAYOUTS: map-merge-r($LAYOUTS, $extension) !global;
  @return layout-get(false, false, $layout-key);
}